Grease a 9x13 inch baking dish with coconut oil or line it with parchment paper, leaving some on the sides to be able to pull up.
If using the marshmallow root powder, combine 1 cup of warm water with the marshmallow root and set aside for 5 minutes (or as long as overnight in the fridge).
Stir well and strain. Make sure that the liquid makes a whole cup, adding more water if necessary.
Pour ½ cup of the prepared marshmallow root infusion into the bowl of a stand mixer. Add the gelatin. Whisk slightly to incorporate and set aside. If not using the marshmallow root simply pour ½ cup of warm water into the mixing bowl, add gelatin, whisk slightly, and set aside.
Pour the other ½ cup of water (or marshmallow root infusion) and 1 cup of honey, and cocoa powder if using, into a small saucepan and whisk to combine.
Slowly bring the water and honey mixture to a boil while stirring. If you have a kitchen thermometer (and I recommend it), you want it to reach at least 240°F. If you don't have a kitchen thermometer, just keep boiling, stirring constantly for 8 minutes.
Turn on the mixer with the liquid/gelatin mixture to medium speed and whisk while slowly pouring the honey/liquid mixture into the mixing bowl.
Once the honey mixture is added, turn the mixer to high and whisk for another 10-15 minutes or until it forms a stiff cream. It should form soft peaks like marshmallow cream. Don't overmix or they can get too hard.
Add the probiotics and any added flavors for the last 2 minutes of mixing.
Once marshmallows are whipped, pour them into the lined/greased dish and smooth out evenly. Damp fingers work well for this.
Let rest for at least 4 hours (overnight is better).
Flip onto a cutting board and cut with a well-oiled pizza cutter or knife.
Store in an airtight container on the counter.
Notes
Do NOT store in the refrigerator as they will melt. Store in an airtight container at room temperature. The probiotics will decrease the shelf life to 3-4 days. Without the probiotics, these will last 2-3 weeks on the counter.